The present invention relates generally to methods and compositions for cementing in well bores.
Hydraulic cement compositions are commonly used in subterranean well completion and remedial operations. For example, hydraulic cement compositions are used in primary cementing operations whereby pipe strings such as casings and liners are cemented in well bores. In performing primary cementing, a hydraulic cement composition is pumped into the annular space between the walls of a well bore and the exterior surfaces of a pipe string disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hard substantially impermeable cement therein. The cement sheath physically supports and positions the pipe string in the well bore and bonds the exterior surfaces of the pipe string to the walls of the well bore, whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented.
Multi-lateral wells have been developed which include vertical or deviated principal well bores having one or more ancillary laterally extending well bores connected thereto. Drilling and completion equipment is available which allows multiple-laterals to be drilled from a principal cased and cemented well bore. Each of the lateral well bores can include a liner cemented therein which is tied into the principal well bore.
While conventional hydraulic cement compositions, which usually include a hydraulic cement (e.g., Portland cement), water, and various conventional cement additives, have been used successfully in primary cementing and other well cementing applications, in some well cementing applications, a cement composition that upon setting has a higher compressive strength and lower permeability than conventional hydraulic cement compositions is desirable. Examples of such well cement applications include, but are not limited to, cemented multi-lateral junctions; kick-off or whip-stock plugs that are placed in a well bore to deflect the drill bit of a drill string and start directional drilling; cement plugs set on top of mechanical bridge plugs used to shut-off lower zones; plugs set in well bores to seal the well bores when the wells are abandoned; and in remedial applications, such as squeeze cementing, where a cement composition is placed with sufficient pressure into cracks, holes or other openings in casings or liners, cement sheaths sealing the liners in the well bore, or the like.